In recent years, hybrid vehicles or electric cars that have a motor as a driving source have been in wide use. It is important to measure a current that flows to the motor when the output of the motor is appropriately controlled. As a method for measuring such a current, for example, there is a method that collects a magnetic field produced around a bus bar according to a current that flows through the bus bar that connects a DC brushless motor and an inverter, using a core made of a magnetic body, detects the magnetic field by a magnetic detecting element, such as a hall element, and calculates and obtains the current that flows through the bus bar on the basis of the detected magnetic field.
On the other hand, in a case where mounting onto hybrid vehicles or electric cars are taken into consideration, a current sensor that measures the current that flows to such a motor requires miniaturization, weight reduction, and multiple connection. By performing miniaturization and multiple connection, the distance between the bus bars that are provided side by side becomes short and the outside dimension of the core also becomes small. Thereby, the linearity of detection sensitivity cannot be ensured or hysteresis characteristics deteriorate. Additionally, disturbance may increase. Thus, techniques described in Patent Documents 1 and 2 that indicate the sources thereof below were studied.
A current sensor described in JP 2008-151743A (Reference 1) is adapted to have a conductor through which a current to be measured flows, an annular magnetic shield plate that is disposed so as to surround the conductor, and has a gap, and a magnetoelectric transducer that is disposed inside the annular magnetic shield plate. The magnetoelectric transducer detects the magnetic flux density of a magnetic field caused by a current. The magnetoelectric transducer is arranged in the vicinity of a position where the magnetic flux density of a magnetic field generated according to a current that flows through the conductor is minimal, between the gap of the annular magnetic shield plate, and the conductor.
A current metering device described in JP 2006-71457A (Reference 2) is adapted to include a magnetic body core, first and second magnetic sensors, and a current detecting circuit. A magnetic body core is arranged so as to surround a current path through which a current flows, and is adapted to include a plurality of gaps. The first and second magnetic sensors are arranged in different gaps, respectively. When the current detecting circuit detects a current that flows through the current path, the residual magnetic flux density of the magnetic body core is corrected from the output of the first magnetic sensor and the output of the second magnetic sensor, to remove an error caused by hysteresis.
A current detecting device described in JP 2006-112968A (Reference 3) is adapted to include a plurality of bus bars through which currents flow, and a plurality of current sensors that detect the currents that flow to the plurality of bus bars. At least some of the plurality of bus bars are provided parallel to each other, and the plurality of current sensors are disposed at positions alternately shifted along the respective bus bars in the bus bars that are provided in parallel.
In the technique described in Reference 1, the magnetoelectric transducer is arranged at a position deviated from a gap end face of the annular magnetic shield plate. Therefore, the effect of increasing the magnetic flux density that the shield plate has, does not reach the inside of the magnetoelectric transducer easily. Therefore, the magnetic flux density to be detected decreases greatly. For this reason, the S/N ratio of the magnetoelectric transducer becomes small. Additionally, since the magnetic flux density decreases, it is necessary to use a high-sensitivity magnetoelectric transducer.
Additionally, in the technique described in Reference 2, two U-shaped magnetic body cores are adapted to have a shape that has two gaps by making opening portions face each other. For this reason, if an external magnetic field is generated, the external magnetic field is collected by the magnetic body core, and the collected magnetic field leads to the opposite magnetic body core through the two gaps. Therefore, a great influence is exerted on the first and second magnetic sensors in the two gaps. In this way, in the technique described in Reference 2, the sensors become susceptible to the external magnetic field.
Additionally, in the technique described in Reference 3, the plurality of current sensors are alternately arranged in a case where detecting parts of the plurality of current sensors, and a magnetic shield are viewed from a position alternately shifted along each bus bar, that is, a direction orthogonal to an extending direction of the bus bar. However, since the magnetic shield is separated from the detecting parts in the shape of Reference 3, the shielding effect is not sufficient. Additionally, in order to enhance the shielding effect, it is necessary to enlarge the magnetic shield in the extending direction of the bus bar. However, in this case, the device will be enlarged.
A need thus exists for a current sensor which is not susceptible to the drawback mentioned above.